Earth Systems — Definition Check Which term refers to the combined portion of the Earth’s surface and the thin layer of air immediately above it that together support life (plants, animals, and microorganisms)?

Introduction / Context:
The study of Earth systems divides our planet into interacting “spheres.” For life-science and geography exams, it is essential to know which sphere directly hosts life. This question checks your ability to identify the zone that includes living organisms and the immediate physical environment that sustains them.

Given Data / Assumptions:

• The focus is on the part of Earth that supports life.
• The phrase includes land surfaces plus a thin overlying air layer.
• We must pick the correct named sphere from standard physical geography terminology.

Concept / Approach:

The biosphere is the global sum of all ecosystems. It spans the lower atmosphere, land surfaces, soils, and shallow waters where organisms live and interact with nonliving components (air, water, minerals). Other atmospheric layers (stratosphere, mesosphere, ionosphere) are defined by temperature or ionization and are not where most life processes occur. Thus, the biosphere uniquely matches the description of life-supporting zones.

Step-by-Step Solution:

Identify keyword “support life” → living systems plus immediate environment.Recall sphere definitions: biosphere (life), atmosphere (air), hydrosphere (water), lithosphere (solid Earth).Match to options: only “biosphere” denotes life’s domain.Eliminate atmospheric layers that are not primarily biological habitats.

Verification / Alternative check:

Ecology texts define the biosphere as the zone of life including the lower atmosphere, land, and waters where organisms exist, confirming the match to the stem’s wording.

Why Other Options Are Wrong:

stratosphere: An atmospheric layer above the troposphere; notable for ozone, not a habitat zone.ionosphere: Upper-atmospheric ionized region affecting radio, not biology.mesosphere: Higher cold layer; again, not the realm of life.

Common Pitfalls:

Confusing “atmosphere” with “biosphere.” The atmosphere includes many layers; only a small lower portion directly hosts life processes in interaction with land and water, which together define the biosphere.

Final Answer:

biosphere